So-called “Yoroigadake lavas”, as named by T. Matsumoto have four lavas and grouped into two types. Namely, one is white rhyolite, the other is black dacite. All lavas have quartz, sanidine and acid plagioclase (An 25-26) as salic phenocrysts. Their chemical and normative mineral compositions are shown in Table 1. Although these lavas resemble to the Haneyama lavas, the Yoroigadake lavas are richer in K2O and poorer in total FeO and Al2O3. In the latter lavas appears C but in the former always appears Wo as norm. From geological age, petrological and petrochemical points, it may safely be said that these lavas have the characters of the Setouchi geologic province.
